1. Field of the Invention
The present invention relates to a magnetic recording medium that is used in hard disk drives, and the method for manufacturing this medium. More particularly, the present invention relates to improvements to a recording medium providing enhanced surface recording densities. Further still, the present invention discloses improvements that increase the density.
2. Description of the Prior Art
Conventional technology offers a magnetic disk medium 60, as shown in FIG. 1A, in which an underlayer 2 is a non-magnetic material, such as chromium, and is deposited on a non-magnetic substrate 1, such as an aluminum substrate. In addition, a magnetic layer 3 composed of an alloy having cobalt as the primary component is formed on the underlayer 2. Furthermore, a protective film 4 such as amorphous carbon is formed on the magnetic layer 3.
In order to increase the track density of the magnetic disk medium, the core width of the magnetic head for recording must be narrowed and the width of a recording track must be reduced. However, in a method which uses a magnetic head to record information, excess recording takes place in the sections (guard bands) between the recording tracks due to the leak magnetic field generated from the side surface of the recording head. This kind of recording is called side erase and is a source of noise during reproduction. The width of the side erase will hardly change unless the gap length and the amount of head flotation are reduced, even if the track density is increased and the core width of the magnetic head for recording is narrowed. Therefore, the signal-to-noise ratio (S/N) during recorded data reproduction becomes hard to guarantee as the track width decreases.
As shown in FIG. 1B, a disk medium 61 in which the tracks 9 are physically separated during manufacturing by forming grooves 8 along the circumferential direction of the disk substrate 1 and guard bands are allocated to the grooves. In this magnetic disk medium 61, if the depth of the grooves is adequate, the leak magnetic field from the recording head does not reach the magnetic layer 3 on the groove 8, and track edge noise is suppressed. This is believed to be effective in increasing the track density.
The width of a guard band is expected to be no more than 0.2 xcexcm as the tracks achieve higher density in the future. Consequently, the groove width must follow this decrease, but there are limitations in the groove forming techniques.
Furthermore, a medium that is formed with grooves has a roughness that causes a height difference ranging from several dozen nanometers to several hundred nanometers on the surface of the medium. In future magnetic disk media, the amount of flotation of the magnetic head will become 30 nm or less as the density increases. In a hard disk drive, air current that is generated by the high-speed rotation of the disk raises the slider that mounts the magnetic head in order to allow the magnetic head to record and reproduce with no contact with the disk. However, if there is roughness on the disk""s surface, turbulence in the air current will produce fluctuations in the level of flotation of the slider, the result of which is instability. This presents a significant problem for the extremely small amounts of flotation of 30 nm or less that is demanded for future magnetic disk media.
One object of the present invention is to provide a magnetic recording medium suited for high-density recording. Another object is to provide a magnetic recording medium that has a high track density. Still another object is to provide a magnetic recording medium that has a high signal to noise ratio. A further object is to provide a magnetic recording medium which reduces writing to the guard bands. Yet another object is to provide a magnetic recording medium that allows lower flotation of the magnetic head.
In keeping with one aspect of the invention, a magnetic recording medium includes a recording layer deposited on a non-magnetic substrate. The recording layer includes a first ferromagnetic layer, a non-magnetic layer, and a second ferromagnetic layer successively deposited on the non-magnetic substrate.
Certain regions of the recording layer are heated to create recording areas in which the first and second ferromagnetic layers are ferromagnetically coupled. The recording areas are separated by non-recording areas in which the first and second ferromagnetic layers are anti-ferromagnetically coupled.
Other objects and advantages of the present invention will be apparent from the following description, the appending claims and accompanying drawings.